Testing arrangement for protected electrical apparatus



July 5, 1949. G. CAMILLI 2,474,825

TESTING ARRANGEMENT FOR PROTECTED ELECTRICAL APPARATUS Filed Feb. 24, 1944 Irfiventorr Guglielmo Carnilli.

His Attorney.

Patented July 5, 1949 TESTING ARRANGEMENT'FOR PROTECTED ELECTRICAL APPARATUS Guglielmo Gamilli, Pittsfield;vMassgi assignordo General Electric Company, a corporation :of New York Application February 24, 1944; SeriaPNof'523L664' 4 Claims Mytinvention relateswto a protectedelectrical apparatus rand-- to an improved arrangement for protecting the apparatusunder overloads, andto an improved method of testing'the'operative condition ofthe protectivearrangement. 5 ingfcoillfi is provided in heat exchange relation Heretofore it has; beencustomary to obtain an theretopand whichiis: connected to the secondary indication of the-hotspot temperatureof an eleo- I! of at current ltransforinent The primary of the tricalrinduction apparatusi such as transformers, current atransfor'rner includes a, conductor la throughra thermal responsive device in the oil which carriesfaload current. In order to provide whiolrdsalsmheatedbya heating coil in response o an: arrangement which"is operative in response to current carnied byi'the transformers A relay to a predetermined?temperature the thermal reresponsive:tosiiohpthermalresponsive device may" spcnsivevdevlcei111135 is provided with a bulb 2t giveramindioation -of the vtemperature of the coils which is surroundedbythecoil l6 and immersed orumay -turn 'oncooling-ifans or may'operate a in the transformer oil. The bulbis connected breaker relay to disconnect the transformer from 5 t La:'suitablerbellows' Within a; thermal relay 2! the-.-c-ircuit-..-:- throughsa tube22in arconventional manner. The bl' fl o y v t0 p ov de an bulb,'wbellows, :and tube contains a suitable fluid proved-1 protective arrangement-for an-electrical 2 hich expandsruponaheatingso that when a pre- DDaixatusmdetermined etemperaturevobtains the bellows will Anothervobject of -myinvention-is to provide operate ani'eoperating iarm 23 for operating a ana-improvedprotectedrelectrical incluction ap-i switch meeh nismezdfi The switch 24 'may acparatusavhichr-is simple in construction, "easy to complish':anysuitablefunction such as being con-- manufacture, and efiicientin operation. nected -to ancoperating relay 25 of a circuit A f -urther objecti-ofmyrinvention is to provide breaker" 2B so that'the transformer may be disanimproved-method of testing-the operative con- 25 connecte'du'ponva predetermined overload time dition of aprotectivedevice -for an electrical in" condition 'havingbeenobtained. Any other suitduotion'apparatusw ablez'numberof thermal relays may be provided,

In -the drawingrl ig; l is a side eleva'tion in andrin the'roonstruction shown in Fig. 1 a second partialrsectionof anielectrical induction xapparatherma'kreIay 'SU-is provided which is adapted to tus whioh is provicled'with an embodiment-of my 0 operate a fan fil so-asto blow air over the cooling, invention; Figs. 2, 3, andw/i illustrate in further coils of the transformers A third thermal. relay detail the -thermal -relay=employed in the system 32 is providedwhich operates a switch to turn on of Fig; 1 andrFigsa5 and fiiill'ustrate curves' w hicn an indicating-Slight 33,- :Anyother suitable therwillibetusedcin describing r myimproved method maluires-ponsive arrangement may be provided in testing the operative conditions of the protec-"35 and thenparticularrthermal responsive device 15 tive-devicet-ew is of the same typewasdescribed and claimed in Referringw-morecr particularly to Fig: 1 of the i it patent -application siN. 517,046',"filed January 5, drawing,-r1;haveillustrated' a protected electrical- 1944, and assigned to thesame-assignee-as this apparatus such as a transformer" which includes prevent-invention. a conventionali windin'g I0 having: a relatively 40 '11 It isto -be.understoodthatin operation the'pro" lowwvoltage bushing?! I anda,irela;tiVely high'volttective device may turn onthe various switches at age bushingilflz" lIhexwinding issurroundedsbyan r mp r 'f r mpl h f m y enclosing casingrfi whichis-filledwith a suitableb rn d on-wh n h =b reaches a p dielectriclor. cooling fluid l4, suchwas transit oil or tureof degrees-G. the light may-be turned on chlorinated-Faromatic hydrocarbona-such as the- 45 :when the =bu1bireaches=l00 degrees (3., and the cirtype disclose'dwrin ChykwPatent 2,041,59,:iissued-- cuit breaker may-.be operated when the bulb or Mayi19,-.1'936;a-nd"whiehds assignedwto the same thermalresponsiverdevice: reaches 115 degrees C. assigneeasthispresentwinvention.- It is tuber-understood.that these temperatures Iniorden to operate a-thermatresponsive device-s co p d o certainhot S1001? temperatures in response a' functionof a suitable tempera- 50 which will usually be higher :than the bulb temtureiofthe rapparatuspsuchvas a hotspotwinda peraturea such:a'thermalresponsive or proteo inn-temperature. so that the apparatus may'optive deviceois suitably-calibrated at the factory eratealongrany suitablepredetermined-over1oadto operate at -temperature such as those listed time icunveha protective-device is provided includabove; It will be understoodyhowever, that it is ingmai thermal responsive device 15 .vvhich is in oo desirabl-eirto :test ithe :protective device such as heat exchange: relation'with a portion of the oil, such as :bybeingkimmersed therein. In order to heat'thethermal responsive device IS in response to a hot-"spot*temperatureof the winding a heatlows.

oint A on the curve of Fig. 5.

temperatures. These methods, however, are open 1.,

to the objection that the protective device could not be tested while the transformer is being operated.

In order therefore to provide an improved arrangement for testing the operative conditions of the protective device, particularly in the field, I provide an auxiliary coil 35 which is adapted to be connected to a suitable potential such as through the leads 3'5 and switch 3'1. Ihe coil 35 may be supported in heat exchange relation I to any suitable part of the thermal responsive arrangement and in construction illustrated more particularly in 2, 3 and i the auxiliary heating coil is attached to the outer casing of the thermal relay El which encloses the bellows 33 through a bracket arrangement Therefore, when it is desired to test the operative condition of the protective device the switch Bl may be closed and a predetermined amount or watts passed through the auxiliary heating coil. 7 relay operates when a predetermined number of watts are transferred to the protective device the operator will know that the protective device onerates satisfactorily.

In order to test the protective device by the method described above the testing device is calibrated in the factory. This may be accomplished in any suitable manner such as by first being sure that the protective device operates satisfactorily, and then calibrating the auxiliary heater by testing in order to see the amount of watts required to operate each of the three belhus forexample, let us assume that the ambient temperature is 30 degrees and it will therefore take a temperature rise of 55 degrees above ambient to operate the thermal relay 3i to turn on the fans. By trial and error the heater 3t: may be heated until the thermal relay so does operate and then the amount of watts necessary to operate the bellows may be recorded, thus giv- In the curve of l 5 it will be seen. that the temperature rise over ambient'in degrees centigrade is plotted as ordinate and the watts necessary for operation of the bellows on the abscissa axis. Points C and B which correspond to relays 2i and 32 may be obtained in similar manner so as to obtain the straight line curve it.

Having the calibration curve as is shown in Fig. 5 it will be seen that my improved method of testing the protective device may be accomplished as follows in the field without disconnecting the transformer from the circuitv The switch Ell may be closed through a potentiometer ll and a watt meter t2, the potentiometer being set so that the number of watts flowing corresponds to point C. if this causes the relay 2i to operate the operator will know the device is operating satisfactorily. Suitable wattage may be employed in order to test the relays til and 32.

Another and more rapid method of testing is to obtain a characteristic curve as is illustrated in Fig. 6 which gives the temperature rise vs. the time the various relays take to operate when a predetermined number of watts is being dissipated by If the .4 the heating coil 35. When the switch 31 is closed the time may be noted in the factory from the time the switch is closed until the relay 2| 0perates in order to obtain point P. Points D and E may be obtained in similar manner for the time it takes for the relays 30 andtZ, respectively, to operate. Two curvesilz and 43 are provided for the maximum and minimum time for operation of the relays for a certain temperature rise. Then in the field the switch may be closed and. if the relays operate in the'various times according to Fig. 6, the operator will know that the protective device is operating satisfactorily. I have found that this is a very efficient method of testing and for instance upon duplicate tests I have found that the various relays close within a range'of about 5 seconds or in the range of the curves given, in Fig. 6. As will be seen in Fig. 1 I provide a separate heating coil 35 for each of the three thermal relays 2|, 3!! and 32, for testing each of the three relays. However, since the bellows in each of the three relays operates through a single closed system, one heater 35 could be used for all the relays, if desired.

With my improved testing arrangement the operator need not take into consideration the actual temperature of the transformer or thermal responsive device l5. Thus 'since the curves of Figs. 5 and 6 give temperature rise over ambient, and also as the thermal system operates upon an increase in pressure of the fluid within the closed fluid system due to an increase in temperature, my testing arrangement operates without regard to the actual temperature of the transformer.

In other words, the fluid pressure in the closed system is a measure of the maximum temperature in the system. Under normal operating conditions the temperature of bulb 2b is higher than the temperature of the bellows 38 because the transformer losses raise itstemperature above that of the ambient. The pressure throughout the system is then a function of the bulb tem perature only and is independent of the temperature of the bellows so that accurate transformer temperature response is obtained without the error which otherwise would occur due to variations in bulb temperature as the latter follows normal variations in ambient temperature. Under test conditions the bellows must therefore be hotter than the bulb and the pressure throughout the system then is a measure of the bellows temperature only and is independent of the temperature of the bulb. From this it follows that the system is a substantially liquid-filled vapor pressure system, i. e., the relatively small amount of the volume in the system not occupied by the liquid is occupied by its vapor. No other system will operate in the above manner. Thus, if the system were entirely liquid filled or entirely vapor filled the pressure would be a measure of the average temperature of the system because the expansion due to heating one part of the system could be cancelled by the contraction due to cooling another part of the system. Under such conditions testing by heating the bellows would be impossible without knowing the bulb temperature. On the other hand, if the system were substantially vapor filled with a relatively small amount of liquid condensate of the vapor in it, then the pressure in the system would be a measure of the minimum temperature or coolest spot in the system because that would be where the liquid would condense out and all the remaining and hotter parts of the system would be vapor filled. Stated difierently, maximum temperature response, as distinguished from average temperature response or minimum temperature response, is obtained only when both liquid and vapor phases of the fluid are in contact with each other where the temperature of the system is a maximum and this means that all the rest and necessarily cooler parts of the system are liquid filled.

Although I have shown and described particular embodiments of my invention, 1 do not desire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

.1. The combination with an electric induction apparatus having an enclosing casing, a cooling fluid in said enclosing casing, a bulb within said enclosing casing and in heat exchange relation to a portion of the cooling medium adapted to be heated by said apparatus, switch means, bellows means for operating said switch means, tube means for connecting said bulb and bellows and providing a closed system, said system being substantially filled with a liquid and the remainder being filled with the vapor of said liquid, of an auxiliary heater means in heat conductive relationship with a part of said closed system which is remote from said bulb, and means for connecting said auxiliary heater means to a source of potential so as to heat said closed system a predetermined amount so as to test the operative condition thereof.

2. The combination with an electric induction apparatus having an enclosing casing, a cooling fluid in said enclosing casing, abulb within said enclosing casing and in heat exchange relation to a portion of the coolin medium adapted to be heated by said apparatus, switch means, bellows means for operating said switch means, tube means for connecting said bulb and bellows and providing a closed system said system being substantially filled with a liquid and the remainder being filled with the vapor of said liquid, of an auxiliary heater means in heat conductive relationship with said bellows, and means for connecting said auxiliary heater means to a source of potential so as to heat said closed system a predetermined amount so as to test the operative condition thereof.

3. The combination with a thermal responsive system of the substantially liquid filled vapor pressure type for protecting encased electric apparatus, said system including a bulb for mounting inside the casing of said apparatus in heat exchange relation with said apparatus, an actuated device for mounting outside said casing, vapor pressure responsive means for mounting outside of said casing connected by a tube to said bulb for actuating said device when the bulb temperature attains a predetermined value, of testing means for said system comprising an auxiliary electric heater in heat exchange relation with said vapor pressure responsive means, and means for selectively causing a predetermined number of Watts to be dissipated in said auxiliary electric heater so as to raise the temperature of said vapor pressure responsive means to a predetermined value which is above the temperature of said bulb so as to test the setting of said system independently of the temperature of said bulb while permitting continuous protected operation of said apparatus.

4. The combination with a thermal responsive system of the substantially liquid filled vapor pressure type for protecting encased liquid cooled and insulated electric induction apparatus, said system including a bulb for mounting inside the casing of said apparatus in heat exchange relation with said liquid, an electric heater for raising the temperature of said bulb above the temperature of said liquid in proportion to the current carried by said apparatus, a circuit controller for mounting outside said casing, vapor pressure responsive means for mounting outside of said casing connected by a tube to said bulb for actuating said circuit controller when the bulb temperature attains a predetermined value, of testing means for said system comprising an auxiliary electric heater in heat exchange relation with said vapor pressure responsive means, and means for selectively causing a predetermined number of watts to be dissipated in said auxiliary electric heater so as to raise the temperature of said vapor pressure responsive means to a predetermined value which is above the temperature of said bulb so as to test the setting of said system independently of temperature of said bulb while permitting continuous protected operation of said apparatus.

GUGLIELMO CAMILLI.

REFERENCES GITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,877,990 Schweitzer Sept. 20, 1932 2,026,079 White et a1 Dec. 31, 1935 2,053,944 Cooney Sept. 8, 1936 2,095,355 Cate Oct. 12, 1937 2,357,353 Pearce Sept. 5, 1944 FOREIGN PATENTS Number Country Date 123,114 Germany Aug. 26, 1901 

